1. Field of the Invention
The present invention relates to an apparatus and method removing mechanical resonance of a system, and more particularly, to an apparatus and method removing mechanical resonance in a disc drive using an adaptive notch filter and varying its frequency characteristics of the filter based on the mechanical resonance frequency existing in the system.
2. Description of the Related Art
Generally, a hard disc drive (HDD) that is a data storage system includes a head disc assembly (HDA) with mechanical components and electronic circuits. Harmful resonance generated in a head stack assembly (HSA) in the HAD appears directly as a position error signal (PES) degrading stability of the servo tracking control of the HDD.
In conventional attempts to solve this problem, the resonance frequency having a harmful influence on the HDD is determined from the frequency of the PES and removed by being filtered or screened. The filters used to remove the determined resonance frequency are designed in an initial development stage based on resonance frequency components identified in the PES of a predetermined number of HDDs. The designed filters are applied commonly to all HDDs.
However, the resonance frequency varies according to the individual characteristics of components in an HSA or the assembly. This variance of the resonance frequency among HSAs having different characteristics results in a problem that cannot be solved by notch filters based on fixed filter coefficients commonly applied to all HDDs.
A conventional technology developed to attempt to solve this problem uses two notch filters 121 and 122, having different frequency characteristics, to remove a resonance frequency, as shown in FIG. 1.
A servo controller 110 uses a PES that is the output signal of a voice coil motor (VCM) actuator 140 to generate a control signal moving the position of a transducer to the center of a target track. The notch filter removes a resonance frequency component in a control signal that may stimulate the VCM actuator 140. Since this resonance frequency varies according to individual characteristics of a transducer, the notch filters 121 and 122 are designed to have different central frequencies to remove major resonant points previously designated through experiments using similar transducers. As a result, a multiplexer 130 selects one of the notch filters 121 and 122, according to an operation of the transducer, to attempt to reduce mechanical resonance.
In the conventional apparatus using two notch filters, each notch filter is also designed to have having characteristics based on a fixed frequency. However, the resonance frequency of an actuator is actually different for each unit. Even in a single unit, resonance varies with respect to a surrounding temperature. Accordingly, due to the fixed central frequency of the notch filters, the related art cannot prevent resonance when the resonance frequency varies according to an operating condition.